Power conversion systems are employed to convert electrical power from one form and/or level, whether AC or DC, to another (AC or DC) in various applications such as pulse width modulated (PWM) current source rectifiers used in high-power motor drives with AC input power being selectively switched to create a DC output bus voltage from which a load is driven. Power converters may include multiple stages for different types of conversion applications, such as AC/DC/AC drives for electric motors, in which input AC power of a given frequency and voltage is first converted to a DC bus, with a second stage selectively switching the DC bus power to create single or multi-phase AC output power of variable voltage and/or frequency. This type of converter is particularly useful in driving electric motors in industrial applications requiring variable speed control with varying motor load situations. In the controlled switching of the input and output power in one or more converter stages, high voltages and currents are experienced by the power switches, where semiconductor-based switches are typically used to switch the power at relatively high frequencies. The control terminals or gates of the switching devices require gate driver circuits to generate the switch signals for actuating the power switch for controlled operation in power conversion applications. In high voltage power conversion applications, the gate driver circuit needs to be operated with power that is isolated from the system ground since the input and output voltages may be several thousand volts or more. Conventional power converters often employ separate isolated DC power sources for powering the gate driver circuits. However, these driver power sources and isolation transformers occupy valuable space and add significant cost in power conversion systems, particularly for medium or high voltage systems operated with GCT or IGCT type switches. Thus, there remains a need for improved power conversion systems and gate driver power sources by which isolated gate driver power can be provided in a cost efficient manner without adding large external power sources.